The present invention relates to a safety device for a machine having a first machine part executing an operational movement towards a second machine part. More particularly, the invention relates to a camera based safety device for a press brake and similar kinds of machines.
DE 10 2004 020 024 A1 discloses a safety device having a light transmitter with a transmission optics and an LED or laser diode as light source. The transmission optics expands the light of the light source to form a light beam. This light beam illuminates a light receiver including an image sensor. The light transmitter and light receiver thus form a light barrier that monitors a protection zone at the lower projecting edge of an upper die on a die press brake. This light barrier is also moved in the operational movement of the upper die in order to detect any dangerous intervention of an object in the work path of the upper die. Whenever an intervention in the protection zone is detected, the known safety device generates signals that result in the die press brake being shut off. DE 10 2004 020 024 A1 purports that the safety device is capable of determining measurement values that relate to individual areas of a workpiece or the die. These measurement values are supposed to be determined by means of the silhouette produced by the workpiece or the die on the light-sensitive elements (pixels) of the image sensor.
For the purpose of determining the measurement values, DE 10 2004 020 024 A1 proposes to define specific pixels of the image sensor as measuring windows which are positioned where silhouette areas with a straight contour are imaged. If appropriate, the measuring windows are supposed to move in the course of the bending process. However, the document does not describe how the measurement values are actually determined. The definition of special measuring windows implies that the algorithm is complex and computational intensive, such that it can be carried out only within relatively small image regions, namely the measuring windows, within the available measuring times. The position and the size of the measuring windows, however, must firstly be determined, and this requires an additional computational outlay. The determination of measurement values which refer to individual areas of a workpiece or the die is therefore not without problems with the known approach.
The assignee of DE 10 2004 020 024 A1, namely Sick AG, 79183 Waldkirch, Germany, offers such a safety device under the brand name V4000. The safety device V4000 uses a laser diode for generating the light beam and is described in detail in an instruction manual available from Sick AG. Interestingly, there is no indication that the safety device V4000 is actually capable of determining measurement values with reference to a workpiece or a die. The V4000 system only operates as a safety device for safeguarding a press brake machine.